You might have simply been seeing the excessive sharpening applied to the original DVD image.

Many DVDs are produced with sharpening and edge enhancement filters applied to them. The idea is to make the DVD look sharp on a small-screen television.

Some DVDs are worse than others in this respect. A recent DVD where this is very noticeable is The Phantom Menace. There is a very visible line at the edge of the letterbox that's caused by oversharpening. This is in the DVD itself. You don't usually notice it until you blow up the image to big-screen size. At smaller sizes, it achieves the desired result and makes the image simply look sharper.

Also, some TVs or DVD players have sharpening filters built into the television, which can cause the same effect or exaggerate the effect if it's encoded into the DVD. Usually this is adjustable on the device in question. For instance, my TV has an easily-selectable "sharpness" setting which allows me to control it.